The objective of this project is to evaluate the cost-effectiveness of an ambulatory drug utilization review (DUR) program with respect to a traditional care process, in terms of quality and economy of prescribing. A quasi-experimental design will apply DUR to a Quebec hospital "A" over an eighteen-month period, and not to a neighboring university hospital "B". In "A", explicit criteria for 50 commonly used prescribed medicines will be discussed by a peer review committee and adapted for approval by prescribers. A 1000 prescriptions from double prescripition pads will be sampled in both institutions for each study quarter. In "A", retrospective computerized screening of sample will be made to determine potential prescribing problems, an in-depth per review conducted and targeted educational feedback given by peers to prescribers. Quality criteria will be rates of prescribing per ambulatory visit, and proportion of prescriptions failing criteria before and after in-depth review. Economy criteria will be differences from base levels in volume and cost of prescribing, the latter being based on the average price for a prescription under the Quebec Drug Program in corresponding quarters. Significance of economic variations from bases levels, between "A" and "B", will be established with a time-series analytical model, which will be developed on a retrospective five-year period with prescription utilization volumes in specialty clinic and in-patient setting within both hospitals. Patient mixes (age, sex and diagnosis) and manpower levels will be accounted for the analysis. The cost-effectiveness of a quality assurance method, ambulatory DUR, may thus be assessed for policy-making.